Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-12-28
2003-12-09
Nguyen, Chau (Department: 2663)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S401000
Reexamination Certificate
active
06661791
ABSTRACT:
BACKGROUND OF THE INVENTION
In a computer network, a networking switch receives a data packet at an ingress port connected to the switch and forwards the data packet to an egress port connected to the switch. The switch determines the egress port to which the data packet is forwarded dependent on a destination address included in a header in the data packet received at the ingress port.
Typically, the switch includes a forwarding table typically implemented in forwarding logic in the ingress engine. The forwarding table is searched for one or more egress ports to which the data packet is to be forwarded dependent on the destination address included in the data packet. However, if the data packet is received for an unknown destination address the switch will not have a matching entry in the forwarding table. Thus, such data packets received at an ingress port are sent to a host processor in the switch; for example, data packets with no matching entry in the forwarding table are forwarded so that the host can update the forwarding table.
One known technique for determining which data packets to forward to the host processor is to make a forwarding decision based on destination address only; for example, to forward all broadcast data packets. If all broadcast data packets are forwarded to the host processor, the host processor may process data packets which may not include information that the host requires. Also, there may be non-broadcast data packets that the host processor requires that are not forwarded to the host. Thus, the forwarding of all broadcast data packets unnecessarily consumes host processor bandwidth and does not provide all the data packets that the host may require.
Another known technique for forwarding data packets to the host processor is to select the data packets to forward based on the data type included in the header of the data packet, such as the type stored in the data link header. The packet types to forward to the host are stored in a host forward list. A data packet is forwarded to the host if the packet type included in the header of the data packet is a member of the host forward list. The host forward list is hardcoded in the switch. In the open systems interconnection, (“OSI”) model, the L
2
packet type is included in the data link layer header.
For example, the L
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packet type may be Address Resolution Type (“ARP”) Bridge Protocol Data Unit, or Internet Protocol (“IP”). This technique reduces the number of data packets forwarded to the host processor by limiting the data packets forwarded to those of a particular type. For example, using the L
2
data type stored in the data link header Bridge Protocol Data Unit data packets may be forwarded only to the host processor, ARP data packets may be forwarded to both the host processor and to the egress port and IP data packets may be forwarded to both the host and the egress port.
The disadvantage is that if a networking protocol with a new L
2
data type is to be forwarded to the host, a new data packet type must be added to the host forwarding list, requiring a hardware update. This technique also may unnecessarily consume host processor bandwidth because not all data packets of a particular L
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data type, such as IP data packets, may be required for processing by the host.
SUMMARY OF THE INVENTION
A memory in a network switch includes at least one forwarding entry having a forward override. Forward override logic in the switch successively searches the memory for forwarding entries matching portions of a received data packet. The forward override logic extracts the forward override from the matching entries. The matching portions of the data packet may be header fields and identify protocols at multiple layers.
The forwarding entry also includes a next field. The forward override logic determines whether to perform another search of the memory dependent on the state of the next field. The memory may be a content addressable memory.
After the search is complete, the forward override logic extracts a forward override for the received data packet from the forwarding entry. Forward select logic in the switch forwards the received data packet dependent on the extracted forward override.
The forwarding entry may include a priority field dependent on the contents of the received data packet and a traffic label field. The traffic label field and the priority field may be forwarded to a host for processing by the host.
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George Keith M.
Hamilton Brook Smith & Reynolds P.C.
MOSAID Technologies Inc.
Nguyen Chau
LandOfFree
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